Ï guess the first step would be to check for literature on this ;-).

If there is not my best guess would be to:

1) hydrolyse the Zink complex by dissolving in methanol acidify mildely (1% acidic acid) dilute say 1:10 in water mix well keep over night

2) extract the stearic acid by shaking with e.g. n-hexane, phase separate (separation funnel), eventually dry and condense

3) add TMSH solution, wait an hour, inject analyse the methyl ester